This invention relates generally to methods and devices for contouring or smoothing freshly poured concrete, sand, gravel, dirt, or other like loose, spreadable materials, and, more particularly, to an apparatus and method for contouring and placement of such materials with a vehicle either positioned adjacent the materials to be contoured or driven through the materials to be contoured.
In the past, the screeding or smoothing of uncured concrete by screeding machines has been primarily limited to flat, one or two dimensional surfaces. In order to screed a three dimensional concrete surface, the screeding apparatus was required to follow predetermined or preset forms, such as wires, boards, or rails, stationed along both sides of the surface to be screeded. Each end of the screed would follow the predetermined physical form By using preset physical forms of different shapes or slopes on either side of the surface to be screeded, it is possible to create a smooth surface having a three dimensional curvature. The use of preset physical forms, however, presents several disadvantages.
The creation of the physical forms is a labor intensive process that increases the time and expense necessary to establish a contoured surface. The preset physical forms also typically only approximate the desired shape of the surface to be contoured, thereby decreasing the quality of the contoured surface. For example, if the physical form consists of a wire, it is virtually impossible to accurately define a desired curvature. Rather, the wire approximates the curvature by a series of successive straight segments. These and other disadvantages of prior screeding techniques have led to the desire to reduce reliance on preset physical forms.
In the past, non-concrete contouring machines have been developed for contouring three dimensional surfaces without the use of preset physical forms. These devices, however, require contact sensors for creating a profile of the subbase over which a material is placed and contoured. These devices have also been limited to earth grading, asphalt laying, or other non-concrete leveling tasks. An example of such a prior device is disclosed in U.S. Pat. No. 5,549,412 issued to Malone. This patent discloses a device for profiling and paving asphalt surfaces in three dimensions. The paving device includes a data storage device for storing the profile of the subbase to be contoured. The accuracy of the profile is dependent upon the frictional and physical characteristics of the contact sensor with respect to the subbase. The contact nature of the sensor may introduce errors into the profile creation that are undesirable.
Some prior art grading machines have also been dependent upon the profile of the subbase. Such machines can only be effectively used after the subbase has been contoured to the desired shape. This increases the amount of work required to screed a concrete surface. Some prior art grading devices have also required the generation of the profile by running the sensors over the subgrade prior to the contouring step. This profile generation step may result in additional inaccuracies due to alignment errors of the contact sensor during the contouring step when compared with the profiling step. This further increases the inaccuracies in the system.
Another disadvantage of the prior art is the required use of multiple sensors to determine the position of the contouring structure in three dimensions. For example, in U.S. Pat. No. 4,807,131 issued to Clegg, a grading system is disclosed that uses a laser reference beam in combination with a pair of wheel encoders. The laser reference beam is used to establish the vertical height of the grading blade while the encoders measure the horizontal position of the grading blade. The use of multiple sensors increases the complexity and associated cost of the grading system, and is therefore undesirable for many applications.